Most ophthalmic lenses dispensed today are made from plastic materials, such as diethylene glycol bisallyl carbonate (CR-39) or polycarbonate. Plastic lenses are inexpensive to fabricate, yet possess good optical properties and are lighter in weight than glass lenses. However, since plastic lenses are easily abraded compared to glass lenses, numerous optical coatings have been developed to improve the abrasion resistance of plastic lenses and to also improve chemical resistance.
A hard coat is usually applied, to the plastic lens using traditional processes such as spin coating, flowing coating, dip coating, spray coating, or other methods. The,coating is then cured using heat or UV radiation after deposition. An alternate method that is applicable for casted products is to simultaneously coat and polymerize both the lens resin and the coating while in the mold. For example, Oshima et al, U.S. Pat. No. 3,968,305, describe a process where the coating material consisting of (a) 20 to 100% by weight of a compound having at least three acryloxy and or methacryloxy groups, with the compound having a chain length of not more than 20 carbon atoms and (b) 0 to 80% by weight of at least one copolymerizable monoethylenically or diethylenically unsaturated compound is first spread over all or part of the inner surface of a mold member. A solid film with little affinity for the coating material is placed above the coating such. that no air bubbles are trapped. The material is then polymerized to an extent that the partially polymerized coating is not dissolved or swelled by the addition of monomer which eventually form the polymeric body. After the pre-polymerization step, the solid film is removed leaving the partially cured coating on the mold surface. The mold is then filled with monomer and fully polymerized resulting in a finished product with an abrasion resistant surface. This process is used to coat polymethyl methacrylate (PMMA) or poly-(diethylene glycol bisallyl carbonate) parts.
Matsuo et al., U.S. Pat. No. 3,968,309, describe the coating material consisting of at least 30% by weight of at least one polyfunctional compound having at least three methacryloxy or acryloxy groups per molecule, and a fluorine-containing surfactant where the fluorine atom is bonded to a carbon atom. An in-mold coating process is described which consists of applying the coating material at a predetermined thickness onto the inner surface of a mold and then irradiating with an energy source in an oxygen-free atmosphere to form a cured film on the inner mold surface. The mold cavity is then filled with a castable material, such as methacrylate syrup or allyl diglycol carbonate and polymerized to obtain a molded article having an abrasion resistant film.
Sandvig et al., U.S. Pat. No. 4,758,448, describe an in-mold coating process for ophthalmic lenses, including multi-focal lenses. The coating material is a mixture of monomers and/or ogligomers with at least one component containing reactive ethylenically unsaturated groups. The coating is applied onto the surface of a mold and reacted so that it forms a dry film but may be tacky to the touch. A degree of unsaturation in the range of about 30 to 90% is required after the initial reaction step. The mold is then filled with a castable material and reacted. Sandvig et al. suggest that in column 2, lines 33-37 that the formation of an abrasion-resistant film on the mold prior to the introduction of the monomer, which is described in Oshima et al., U.S. Pat. No. 3,968,305, would not work for the in-mold curing process.
Sandvig et al. also describe problems with the performance of the coating if, during the partial reaction step, the film is not properly cured. For example, if the film under cured, the resulting system shows poor abrasion resistance and maybe hazy. Sandvig et al., suggest that the coating be at least 10% cured prior to the casting of the lens, and during this initial curing process, the resulting film may be tacky to the touch, but must be dry.
Carmelite et al., U.S. Pat. No. 4,774,035, describe a coating material composed primarily (80 to 95% by weight) of reactants having at least a triacrylate functionality and between 5 to 20% by weight of a diacrylate reactant, photoinitiator, polymerization inhibitor, silane adhesion promoter and an acid to activate the adhesion promoter. The adhesion promoter is used to obtain better adhesion between the coating material and metal or glass molds to reduce defects associated with delamination of the coating material from the mold face. The coating is applied to the mold surface as described in the previous patents utilizing an in-mold curing process, and polymerized in air such that a hard abrasion resistant coating is formed on the mold. The mold cavity is then filled with the lens forming resin and cured.
Finally, Galic, U.S. Pat. No. 5,049,321 (1991), describes an in mold coating process similar to that of Carmelite et al. The coating is first applied to the inner mold surface and partially cured in air such that the reactants are substantially polymerized to form a hard abrasion resistant state but with sufficient acrylate functionality at the lens/coating interface for further reaction. The mold cavity is filled with the lens forming resin and cured completely.